Electrical measuring instrument.



G. HERING. ELECTRICAL MEASURING INSTRUMENT.

APPLICATION FILED AUG-3. 1905.

PATEN'TED SEPT. 25, 1906.

W716 686 a: jz'aeizzorx UNITED STATES PATENT OFFICE.

CARL HERING, OF PHILADELPHIA, PENNSYLVANIA.

ELECTRICAL MEASURING INSTRUMENT.

Specification of Letters Patent. Application filed August 3, 1905. Serial No. 272,608.

No. 831,609 Patented Sept. 25, 1906.

To all whmn it may concern.-

Be it known that I, CARL HERING, a citijust overbalances this attraction when the current has the standard value. At that me- Zen of the United States, residing at 929 ment the movable coil will fall away from the Chestnut street, in the city of Philadelphia, l fixed one, thereby indicating when the curcounty of Philadelphia, and State of Pennrent has its standard value. T 0 use the insylvania, have invented certain new and usestrument, the current is first made greater iul Improvements in Electrical Measuring Inthan the standard value, the movable coil struments, of which the following is a specij being thereby held up against the fixed one. fication. The current is then diminished very gradu- The object of my invention is to produce a ally until the movable coil drops. At exsimple and convenient instrument based on actly that moment the current has the standpurely mechanical and electrical principles ard value. It is intended to be used as a seewhich will indicate with great precision and ondary standard to calibrate current-measconstancy when an electrical current has a uring instruments for that particular value. certain definite strength, thereby enabling The measuring instrument to' be calibrated the usual electrical-current-measuring instruis placed in series with it and its reading is ments to be tested for accuracy and to be re taken at the moment when the coil drops. calibrated. It is particularly intended to be My instrument can be made for indicating used as a concrete standard ampere and beany one particular value. Hence with sevlongs to the same class of instruments as the eral of them several pomts can be calibrated concrete standard ohm and the concrete on the measuring instrument which is to be standard cell, as it indicates only a singleadjusted, or by the adjustment of countercurrent strength, but does this with great weights to partly balance the weight of the precision and constancy and is not dependcoil or by means of shunts the same apparaent on the constancy of steel magnets or tus may be used to indicate several standard springs, which are apt to change their values currents. It may also be used indirectly as in time, and therefore cannot be relied upon a standard of voltage for calibrating voltas remaining constant. It is also independmeters by connecting the voltmeter to be ent of any chemical action or temperature calibrated to the ends of a known resistance and can be used for both direct and alternat through which a current is passing, which ouring currents. rent is then standardized by means of my Heretofore currents for standardizing instandard concrete ampere. Knowing the restruments have usually been measured with sistance and the current the voltage becomes a voltameter or with a potentiometer. The known by Ohms law. This method has the former besides being cumbersome involves advantage of great simplicity, rapidity, can chemical reactions and the latter a standard be carried out at the switchboard, and recell and a standard ohm besides a somewhat quires no standard cell, galvanometer, or pocomplicated apparatus. Both are subject to tentiometer. hen so used, it may be calicorrections, such as those for temperature, brated to read in volts directly, or it may be and .both require skilled operators. My inused directly as a volt standard by winding vention overcomes all these objections. It the coils with many turns of fine wire, giving is capable of being used in central stations i the instrument ahigh resistance and connect and by unskilled operators, is complete in ing it acrossthetwoterminals otthevoltmeter itself, simple to handle, is not based on indito be calibrated. The current which acturect measurements like those usually used, ates it will then be proportional to the volrequires no corrections like that for temperatage if the resistance of the instrument reture, and is simple in construction and cheap. mains constant, or it maybe made to indicate It is based on the dynamonieter principle- I watts by the usual method of passing the namely, on the mutual attraction of two coils main current through one of the coils, while through which the current to be measured through the other is passed as shunt-current passes. One of these 0011s is fixed, and the which is proportional to the voltage. other is movable. The movable one is held As the action of the instrument depends up against the lower side of the fixed one by on nothing but the attraction of the current the attraction due to the currents in both..

to itself, it is equally applicable to direct and Its weight is so adjusted by the maker that it to alternating currents,

also to pulsating or intermittent currents. It. indicates their effective values as distinguished from their mean values. As the attraction between two such coils is proportional to the product of the currents, and therefore to the square of the current when both coils are in series, it follows that the force which holds them together varies much more rapidly than the current. Hence the instrument becomes very sensitive to variations of the currents and may therefore be made to give a very accurate sharplydefined indication of the standard value. At the moment when the movable coil begins to drop even by only the slightest amount the distance from the other coil begins to increase, which then diminishes the attraction between them, and this diminution rapidly becomes greater as the coil falls, thereby making the indication a sharply-defined one, or, in other words, the coil is balanced in unstable equilibrium, and as soon as it begins to move the motion increases rapidly. When the current passes through both coils in series, it is evident that no corrections'such as those for temperature are required. The only correction is that for the variations of the force of gravity due to difference of latitude and elevation. These are very slight, and as they are definite and fixed values they can be readily allowed for when such extreme accuracy is desired.

For a full understanding of my invention reference is made to the accompanying drawings, wherein Figure 1 is a vertical crossssection of the instrument in its general form and a diagrammatic representation of its connection in circuit. Fig. 2 shows a modified form of the mounting and appurtenances of the moving coil.

In Fig. 1, F is the fixed coil. M is the movable coil below it. The coils are here shown as flat and circular; but they may of course be made of any desired cross-section and shape. They may, for instance, be made oblong and the fixed one may be given many turns, while the movable one may have few turns or even only one turn in order to make it light. For lightness the lower one may be made of aluminium. S S are stops which limit very precisely the distance between the coils when they are brought together- They ought not to be made of steel, as all magnetic materials should be excluded. They may be made of glass rounded at their ends. The ends need not be pointed. There should be three of these when the mounting is of the form shown in Fig. 1, and they should have corresponding sockets above to insure the coils being in exactly the same relative position each time they are brought together. The diagrammatic connections show that. the two coils are in series. A is the ammeter to be calibrated. It is placed in series with the standardizing instrument. R and R are adjustable resistances which may be either in series or shunt or one in each for gradually diminishing the current until it reaches the standard value.

A current suflicient to sustain the weight of the coil through which it flows is apt to heat it. For this and for other reasons, such as mechanical considerations, &c., I prefer to mount the coil as shown in Fig. 2, in which its weight is partly balanced by the counterweight W, the whole being suspended by the strap or straps P. This has many other advantages also. If there are two supportingstraps or wires P, they may be used to lead the current to and from the movable coil. If they are free from any initial set, their spring action does not affect the indications of the instrument, for the moment there is the slightest movement of the coil it will drop, even if a slight spring action opposes it after it starts dropping. These straps may be replaced by knife-edges or horizontal torsion-wires or any of the well-known equivalents of pivots. If knife-edges are used, flexible connections for conducting the current may best be made near the knife-edges to avoid any spring action of those connec tions, or mercury-cups may be used, in which case the level of the mercury had better be the same as that of the horizontal turning axis to reduce the effects of unequal surface tensions. The weight W is best made adjustable, giving the maker a con venient means of adjusting the indication of the instrument to an exact current. By the addition of other properly-adjusted weights, like W, the same instrument may be made to indicate several currents of different values, thereby enabling several points on the scale of an ammeter to be calibrated, or one weight may be moved to several indi cated positions on its guide. Diflerent ranges of the instrument may also be obtained by inclining both coils at different angles in a vertical plane or by means of numerous other evident equivalents.

The indicator I opposite to a fixed mark ICC indicates when the coil has dropped and enables the coil to be raised again for repeating the reading. A bell B may be used to indicate the drop by being struck by the moving part, or a contact closing an auxiliary electric circuit of a bell or buzzer may be used as an indicator, or any other evident equivalent may be used to indicate the drop. When not in use or while being shipped, the rod I may be clamped, so as to prevent the coil from moving.

The constant of the instrument may also be adjusted by varying the distance between the coils by means of the stops S.

For use with alternating or pulsating currents I may connect the moving coil to a damper or a mass having considerable inertia, so that the dropping of the coil is not aotuated by the rapid fluctuations of the current, but only by the slowly decreasing effective value.

The expression the weight of the movable coil being equal to the magnetic attraction between said coils when traversed by the current to be measured is used in the claims to express the relation heretofore described-via, that the weight of the movable coil when it is supported by the magnetic attraction alone, as in the arrangement shown in Fig. 1, or the effective weight of the movable coil when it is partially counterbalanced, as shown in Fig. 2, must be such that it just overbalances the magnetic attraction due to the currents in both coils when the current has the standard value.

I claim 1. An electrical measuring instrument comprising fixed and movable coils, said movable coil adapted to be held in a definite position of unstable equilibrium by current in excess of a definite value traversing said coils and adapted to be released by a current less than this definite value and to drop beyond the control of the fixed coil, substantially as described.

2. An electrical measuring instrument comprising fixed and movable coils, and means for partially counterbalancing the movable coil, said movable coil adapted to be held in a definite position of unstable equilibrium by current in excess of a definite value traversing said coils and adapted to be released by a current less than this definite value and to drop beyond the control of the fixed coil, substantially as described.

3. An electrical measuring instrument com prising fixed and movable coils, and means comprising an adjustable counterweight for partially counterbalancing said movable coil, said movable coil adapted to be held in a definite position of unstable equilibrium by current in excess of a definite value traversing said coils and adapted to be released by a current less than this definite value and to drop beyond the control of the fixed coil, substantially as described.

4. An electrical measuring instrument comprising a fixed coil, and a movable coil adapted to be held in a position of unstable equilibrium and in definite relation to said fixed coil by current in excess of a definite value traversing said coils and adapted to be re leased by a current less than this definite value and to move beyond the control of the fixed coil, substantially as described.

5. An electrical measuring instrument comprising a fixed coil, a movable coil adapted to be held in a position of unstable equilibrium and in definite relation to said fixed coil by current in excess of a definite value traversing said coils and adapted to be released by a current less than this definite value and to move beyond the control of the fixed coil, and means for partially counterb al ancing said movable coil, substantially as described.

6. An electrical measuring instrument comprising a fixed coil, a movable coil adapted to be held in a position of unstable equilibrium and in definite relation to said fixed coil by current in excess of a definite value traversing said coils and adapted to be released by a current less than this definite value and to move beyond the control of the fixed coil, and an adjustable counterweight for partially counterbalancing said movable coil, substantially as described.

7. An electrical measuring instrument comprising fixed and movable coils, said movable coil adapted to be held in a position of unstable equilibrium by current in excess of a definite value traversing said coils, and a device for indicating the drop of the movable coil when the current reaches a definite value, substantially as described.

8. An electrical measuring instrument comprising a fixed coil, a movable coil ada ted to be held in a position of unstable equi ibrium and in definite relation to said fixed coil by current in excess of a definite value traversing said coils, adjustable means for partially counterbalancing said movable coil, and a device for indicating the drop of the movable coil when the current reaches a definite value, substantially as described.

9. An electrical measuring instrument comprising fixed and movable coils, said movable coil adapted to be held in a definite position of unstable equilibrium by current in excess of a definite value traversing said coils, and adapted to be released by a current less than this definite value and to drop beyond the control of the fixed coil, and means for limiting the minimum distance between said coils, substantially as described.

10. An electrical measuring instrument comprising fixed and movable coils, the effective weight of the movable coil being equal to the magnetic attraction between said coils when they are at a certain definite distance apart and when traversed by the current to be measured, substantially as described.

11. An electrical measuring instrument comprising fixed and movable coils, and means for limiting the minimum distance between said coils, the ell'ective weight of the movable coil being equal to the magnetic attraction between said coils when they are at this minimum distance apart and when traversed by the current to be measured, substantially as described.

12. An electrical measuring instrument comprising fixed and movable coils, means for limiting the minimum distance between said coils, supporting means for said movable coil permitting movement thereof about an axis, and means for partially counterbalancing said movable coil, the excess of weight of ICC said movableeoil beingequal to the magnetic attraction between said coils when they are at this minimum distance apart and when traversed by the current to be measured, sub stantially as described,

13. An electrical measuring instrument comprising fixed and movable coils, means for limiting the minimum distance between said coils, supporting means for said movable coil permitting movement thereof about an axis, and adjustable means for partially countel-balancing said movable coil, the excess of CARL HERING.

Witnesses:

ERWIN F. FABER, MARION R. FARER. 

